Sterling principle

Cortel, Tine, Theo Stevens, David Newton, and Charles Abbot. Basic Principles and Language of Fine Art. New York Distributed by Sterling, 1989. 

Figure 23.18 From Bliss, G. (2001) Practical Solutions for Potters. Sterling Pub Co. Inc. New York, p. 103. Table 23.3 Data compiled by Reed, J.S. (1988) Introduction to the Principles of Ceramic Processing, John Wiley, New York, p. 359.

Before the 1970 s, if a winder was powered by a DC motor or motors, the control of the motor(s) would have been almost exclusively by MG sets operating on the Ward Leonard principle. English Electric and AEI did, however build a limited number of winder drives using mercury arc rectifiers. Preference by some mine operators for Ward Leonard drives even lasted well into the 1980 s and many of those winders are still rendering sterling service today. 

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